Light emitting device

ABSTRACT

A light emitting device includes an active layer; at least a portion of the active layer constitutes a gain region. The gain region is continuous from a first end surface and a second end surface. The gain region includes a first portion extending from the first end surface to a first reflective surface in a direction tilted with respect to a normal to the first side surface as viewed two-dimensionally; a second portion extending from the second end surface to the second reflective surface in a direction tilted with respect to a normal to the first side surface as viewed two-dimensionally; and a third portion extending from the first reflective surface to the second reflective surface in a direction tilted with respect to a normal to the first reflective surface as viewed two-dimensionally.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. Ser. No. 13/307,329 filedNov. 30, 2011, which is a continuation of U.S. Ser. No. 12/687,337 filedJan. 14, 2010, now U.S. Pat. No. 8,089,088 issued Jan. 3, 2012 whichclaims priority to Japanese Patent Application No. 2009-018306 filed onJan. 29, 2009, all of which are hereby incorporated by reference intheir entireties.

BACKGROUND

1. Technical Field

The present invention relates to a light emitting device.

2. Related Art

Laser devices having high luminance and excellent color reproductionproperties have been anticipated in recent years as light emittingdevices for use as light sources for projectors, displays, and otherdisplay devices. However, speckle noise that occurs from mutualinterference of scattered and reflected light at the screen surface issometimes problematic. In order to address this problem, a method hasbeen proposed in Japanese Laid-Open Patent Publication No. 11-64789, forexample, in which the screen is vibrated to uniform the speckle patternand thereby reduce the speckle noise.

SUMMARY

However, in the method disclosed in Japanese Laid-Open PatentPublication No. 11-64789, new problems sometimes occur, such aslimitation of the screen, the need for a motor or other member formoving the screen, and background sound from the motor or the like.

A common LED (Light Emitting Diode) may also be used as the lightemitting device for the light source in order to reduce speckle noise.However, adequate light output is sometimes not obtained from an LED.

An advantage of the present invention is to provide a novel lightemitting device having high output and the capability of reducingspeckle noise.

A light emitting device according to a first aspect includes a firstcladding layer, an active layer formed above the first cladding layer,and a second cladding layer formed above the active layer. At least aportion of the active layer constitutes a gain region. The gain regionis continuous from a first end surface provided to a first side surfaceof the active layer to a second end surface provided to the first sidesurface. The gain region has a first reflective surface and a secondreflective surface for reflecting light generated by the gain region,and the first reflective and the second reflective surface enable thegain region to extend from the first end surface to the second endsurface. The gain region includes a first portion extending from thefirst end surface to the first reflective surface in a direction tiltedwith respect to a normal to the first side surface as viewedtwo-dimensionally; a second portion extending from the second endsurface to the second reflective surface in a direction tilted withrespect to a normal to the first side surface as viewedtwo-dimensionally; and a third portion extending from the firstreflective surface to the second reflective surface in a directiontilted with respect to a normal to the first reflective surface asviewed two-dimensionally. A distributed Bragg reflector or a photoniccrystal region is provided to at least one of a side of the firstreflective surface and a side of the second reflective surface. At leasta portion of the light generated by the gain region that passes throughthe first reflective surface or the second reflective surface isreturned to the gain region by the distributed Bragg reflector orphotonic crystal region. The light generated by the gain region isemitted from the first end surface and the second end surface.

In the light emitting device according to the first aspect of thepresent invention, laser oscillation of light generated by the gainregions can be suppressed or prevented, as described hereinafter.Speckle noise can therefore be reduced. Furthermore, in the lightemitting device according to the first aspect of the present invention,the light generated by the gain regions can be amplified whilepropagating in the gain regions, and be emitted to the outside.Consequently, a higher output than that of the conventional LED can beobtained. Through the present invention as described above, a novellight emitting device can be provided that has high output and thecapability of reducing speckle noise.

In the description of the present invention, the wording “above” is usedto denote that “a specific member (hereinafter referred to as “memberB”) is formed “above” another specific member (hereinafter referred toas “member A”),” for example. In the description of the presentinvention, in a case such as the one illustrated by the example above,the wording “above” is used to include such cases as when member B isformed directly on member A, and such cases as when member B is formedvia another component on member A.

In the light emitting device according to a second aspect of the presentinvention, a configuration may be adopted in which the first reflectivesurface of the gain region is parallel to the first side surface of theactive layer as viewed two-dimensionally, the normal to the firstreflective surface and the normal to the second reflective surface areorthogonal, and the distributed Bragg reflector or the photonic crystalregion is provided to a side of the second reflective surface.

In the light emitting device according to a third aspect of the presentinvention, the light generated by the gain region may be totallyreflected by the second reflective surface.

In the light emitting device according to a fourth aspect of the presentinvention, the direction in which the first portion extends and thedirection in which the second portion extends may be the same direction.

In the light emitting device according to a fifth aspect of the presentinvention, the distributed Bragg reflector may include a plurality ofgrooves arranged at a predetermined interval.

In the light emitting device according to a sixth aspect of the presentinvention, a bottom surface of the grooves may be positioned furtherdownward than a lower side surface of the active layer.

In the light emitting device according to a seventh aspect of thepresent invention, the photonic crystal region may include a pluralityof holes arranged periodically in a predetermined lattice arrangement inthe in-plane direction of the active layer.

In the light emitting device according to an eighth aspect of thepresent invention, a configuration may be adopted in which the shape ofeach of the plurality of holes is columnar, and a bottom surface of theholes is positioned further downward than a lower surface of the activelayer.

In the light emitting device according to a ninth aspect of the presentinvention, an antireflective film may be provided to the first sidesurface.

In the light emitting device according to a tenth aspect of the presentinvention, a plurality of the gain regions may be provided.

The light emitting device according to an eleventh aspect of the presentinvention may include a first electrode electrically connected to thefirst cladding layer; and a second electrode electrically connected tothe second cladding layer.

In the description of the present invention, the wording “electricallyconnected” is used to describe a specific member (hereinafter referredto as “member D”) that is “electrically connected” to another specificmember (hereinafter referred to as “member C”),” for example. In thedescription of the present invention, in a case such as the oneillustrated by the example above, the wording “electrically connected”is used as including such cases as when member C and member D aredirectly adjacent and electrically connected to each other, and suchcases as when member C and member D are electrically connected viaanother member.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a schematic perspective view showing the light emitting deviceaccording to the first embodiment;

FIG. 2 is a schematic plan view showing the light emitting deviceaccording to the first embodiment;

FIG. 3 is a schematic sectional view showing the light emitting deviceaccording to the first embodiment;

FIG. 4 is a plan view showing the active layer according to the firstembodiment from the side of the first side surface;

FIG. 5 is a graph showing the wavelength dependence of the reflectanceof the DBR of the first embodiment;

FIG. 6 is a schematic sectional view showing the steps for manufacturingthe light emitting device of the first embodiment;

FIG. 7 is a schematic sectional view showing the steps for manufacturingthe light emitting device of the first embodiment;

FIG. 8 is a schematic sectional view showing the steps for manufacturingthe light emitting device of the first embodiment;

FIG. 9 is a schematic plan view showing a first modification of thelight emitting device according to the first embodiment;

FIG. 10 is a schematic sectional view showing a first modification ofthe light emitting device according to the first embodiment;

FIG. 11 is a schematic plan view showing a second modification of thelight emitting device according to the first embodiment;

FIG. 12 is a schematic plan view showing the light emitting deviceaccording to the second embodiment;

FIG. 13 is a schematic sectional view showing the light emitting deviceaccording to the second embodiment;

FIG. 14 is a schematic sectional view showing the steps formanufacturing the light emitting device of the second embodiment; and

FIG. 15 is a schematic sectional view showing a modification of thelight emitting device according to the second embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinafter with reference to the drawings.

1. First Embodiment

1.1. The light emitting device 100 according to a first embodiment willfirst be described.

FIG. 1 is a schematic perspective view showing the light emitting device100. FIG. 2 is a schematic plan view showing the light emitting device100. FIG. 3 is a sectional view along line III-III of FIG. 2. The secondelectrode 122 and the antireflective film 114 are omitted in FIG. 1 forthe sake of convenience. The second electrode 122 is omitted in FIG. 2for the sake of convenience. A case is described in which the lightemitting device 100 is an InGaAlP-type (red) semiconductor device.

As shown in FIGS. 1 through 3, the light emitting device 100 includes afirst cladding layer 104, an active layer 106, and a second claddinglayer 108. The light emitting device 100 may further include a substrate102, a contact layer 110, an insulation part 112, an antireflective film114, a first electrode 120, a second electrode 122, and a distributedBragg reflector (also referred to hereinafter as a DBR) 170.

A first conductive (e.g., n-type) GaAs substrate or the like, forexample, may be used as the substrate 102.

The first cladding layer 104 is formed on the substrate 102. The firstcladding layer 104 is composed of a first conductive semiconductor, forexample. An n-type AlGaInP layer or the like, for example, may be usedas the first cladding layer 104. Although not shown in the drawing, abuffer layer may be formed between the first substrate 102 and the firstcladding layer 104. A first conductive (n-type) GaAs layer, InGaP layer,or the like, for example, having more satisfactory crystal properties(e.g., low defect density) than the substrate 102, for example, may beused as the buffer layer.

The active layer 106 is formed on the first cladding layer 104. Theactive layer 106 has a multiple quantum well (MQW) structure in whichthree quantum well structures composed of an InGaP well layer and anInGaAlP barrier layer are stacked, for example.

A portion of the active layer 106 constitutes a gain region. The gainregion 140 is capable of generating light, and this light can beamplified within the gain region 140. The active layer 106 may have arectangular (including cuvic) or other shape, for example. The activelayer 106 has a first side surface 105 and a second side surface 107.The first side surface 105 and second side surface 107 are parallel toeach other, for example.

The gain region 140 is continuous from a first end surface 151 providedto the first side surface 105 of the active layer 106 to a second endsurface 152 provided to the first side surface 105. The gain region 140also may have a first reflective surface 160 and a second reflectivesurface 162 for reflecting the light generated by the gain region 140,between the first end surface 151 and the second end surface 152. Thegain region 140 is composed of a first portion 142, a second portion144, and a third portion 146. The first portion 142 extends from thefirst end surface 151 to the first reflective surface 160 in a directiontilted with respect to the normal P1 of the first side surface 105 asviewed two-dimensionally (see FIG. 2). The second portion 144 extendsfrom the second end surface 152 to the second reflective surface 162 ina direction tilted with respect to the normal P1 of the first sidesurface 105 as viewed two-dimensionally. The third portion 146 extendsfrom the first reflective surface 160 to the second reflective surface162 in a direction tilted with respect to the normal P2 of the firstreflective surface 160 as viewed two-dimensionally. Laser oscillation ofthe light generated by the gain region 140 can thereby be suppressed orprevented. The light emitting device 100 can therefore generate lightthat is not laser light.

The first portion 142 has the first end surface 151 provided to thefirst side surface 105, and a third end surface 153 that constitutes thefirst reflective surface 160. The first portion 142 extends from thefirst end surface 151 to the third end surface 153 in a direction Ahaving a tilt of angle θ₁ with respect to the normal P1 of the firstside surface 105, as shown in FIG. 2. The direction A in which the firstportion 142 extends can be referred to as the direction in which thecenter of the first end surface 151 and the center of the third endsurface 153 are connected as viewed two-dimensionally, for example. Theplanar shape of the first portion 142 is a parallelogram, for example.

The second portion 144 has the second end surface 152 provided to thefirst side surface 105, and a sixth end surface 156 that constitutes thesecond reflective surface 162. The second portion 144 extends from thesecond end surface 152 to the sixth end surface 156 in a direction Bhaving a tilt of angle θ₂ with respect to the normal P1 of the firstside surface 105, as shown in FIG. 2. The direction B in which thesecond portion 144 extends can be referred to as the direction in whichthe center of the second end surface 152 and the center of the sixth endsurface 156 are connected as viewed two-dimensionally, for example. Theplanar shape of the second portion 144 is a trapezoid in which the twoend surfaces other than the second end surface 152 and the sixth endsurface 156 are parallel to each other, for example. The direction A inwhich the first portion 142 extends and the direction B in which thesecond portion 144 extends are the same direction in the example shown.The first emitted light 20 emitted from the first end surface 151 andthe second emitted light 22 emitted from the second end surface 152 canthereby proceed in the same direction. Although not shown in thedrawing, the direction A in which the first portion 142 extends and thedirection B in which the second portion 144 extends may also be mutuallydifferent.

The third portion 146 has a fourth end surface 154 that constitutes thefirst reflective surface 160, and a fifth end surface 155 thatconstitutes the second reflective surface 162, as shown in FIG. 2. Thethird portion 146 extends from the fourth end surface 154 to the fifthend surface 155 in a direction C having a tilt of angle θ₃ with respectto the normal P2 of the first reflective surface 160, as shown in FIG.2. The direction C in which the third portion 146 extends can bereferred to as the direction in which the center of the fourth endsurface 154 and the center of the fifth end surface 155 are connected asviewed two-dimensionally, for example. The planar shape of the thirdportion 146 is a trapezoid in which the two end surfaces other than thefourth end surface 154 and the fifth end surface 155 are parallel toeach other, for example.

FIG. 4 is a view showing the active layer 106 in a plane as viewed fromthe side of the first side surface 105. As shown in FIG. 4, the thirdend surface 153 and the first end surface 151 of the first portion 142do not overlap. The light generated by the first portion 142 thereby canbe prevented from directly undergoing multiple reflection between thefirst end surface 151 and the third end surface 153. As a result, sincethe creation of a direct resonator can be prevented, laser oscillationof the light generated by the first portion 142 can be more reliablysuppressed or prevented. In this case, it is sufficient insofar as theoffset width x between the first end surface 151 and the third endsurface 153 is a positive value in the gain region 140, for example, asshown in FIG. 4. In the example shown in FIG. 4, the second end surface152 of the second portion 144, and the fourth end surface 154 of thethird portion 146 are overlapped. As shown in FIG. 2, the region inwhich the second end surface 152 and the fourth end surface 154 aredirectly connected includes a region in which the second portion 144 andthird portion 146 are not formed. Such a region in which the gain regionis not formed is an absorption region. Therefore, even if directmultiple reflection occurs between the second end surface 152 and thefourth end surface 154, adequate gain for oscillation cannot beobtained. In the example shown in FIG. 4, the second end surface 152 andthe fourth end surface 154 are partially overlapped, but the second endsurface 152 and the fourth end surface 154 may also be arranged so asnot to overlap. Oscillation can thereby be prevented at higher outputsas well.

The first reflective surface 160 is composed of the third end surface153 of the first portion 142, and the fourth end surface 154 of thethird portion 146. In the example shown, the third end surface 153 andthe fourth end surface 154 completely overlap each other, and the firstreflective surface 160 coincides with the third end surface 153 and thefourth end surface 154. Although not shown in the drawing, the third endsurface 153 and the fourth end surface 154 may partially overlap eachother. The first reflective surface 160 may be parallel to the firstside surface 105 as viewed two-dimensionally (see FIG. 2). The angle θ₄formed by the normal P2 of the first reflective surface 160 and thedirection A in which the first portion 142 extends, and the angle θ₃formed by the normal P2 of the first reflective surface 160 and thedirection C in which the third portion 146 extends are equal, forexample. A DBR 170 is provided on the side of the first reflectivesurface 160 in the example shown in FIG. 2. A high reflectance canthereby be obtained from the first reflective surface 160. Although notshown, a dielectric minor may be provided on the side of the firstreflective surface 160 instead of the DBR 170 by adopting aconfiguration in which the first reflective surface 160 is formed by thesecond side surface 107 by a cleavage or other technique.

The second reflective surface 162 is composed of the fifth end surface155 of the third portion 146, and the sixth end surface 156 of thesecond portion 144. In the example shown, the fifth end surface 155 andthe sixth end surface 156 completely overlap each other, and the secondreflective surface 162 coincides with the fifth end surface 155 and thesixth end surface 156. Although not shown in the drawing, the fifth endsurface 155 and the sixth end surface 156 may partially overlap eachother. The normal P2 of the first reflective surface 160 and the normalline P3 of the second reflective surface 162 are orthogonal in theexample shown. The angle θ₅ formed by the normal line P3 of the secondreflective surface 162 and the direction C in which the third portion146 extends, and the angle θ₆ formed by the normal line P3 of the secondreflective surface 162 and the direction B in which the second portion144 extends are equal, for example. The light generated by the gainregion 140 may undergo total reflection at the second reflective surface162, for example. A case in which the light generated by the gain region140 is totally reflected at the second reflective surface 162 is a casein which the angle θ₆ of the direction B in which the second portion 144extends and the angle θ₅ of the direction C in which the third portion146 extends with respect to the normal line P3 of the second reflectivesurface 162 are each equal to or greater than a critical angle θ_(C),for example. The DBR 170 may be provided on the side of the secondreflective surface 162, as shown in FIG. 2. A high reflectance canthereby be obtained from the second reflective surface 162. Thescattered light that could not be totally reflected at the secondreflective surface 162 can also be returned to the DBR 170, for example.Although not shown, a dielectric minor may be provided instead of theDBR 170 on the side of the second reflective surface 162 by adopting aconfiguration in which the second reflective surface 162 is formed by aside surface of the active layer 106 other than the first side surface105 and second side surface 107 of the active layer 106 through the useof a cleavage or other technique, for example.

The reflectance of the first reflective surface 160 and secondreflective surface 162 is preferably higher than the reflectance of thefirst end surface 151 and second end surface 152 in the wavelength rangeof the light generated by the gain region 140. Specifically, thereflectance of the first reflective surface 160 and second reflectivesurface 162 is preferably close to 100%. In contrast the reflectance ofthe first end surface 151 and second end surface 152 is preferably closeto 0%. Providing the antireflective film 114, for example, enables lowreflectance to be obtained from the first end surface 151 and second endsurface 152. The antireflective film 114 may be provided to the entiresurface of the first side surface 105. An Al₂O₃ single layer, an SiO₂layer, an SiN layer, a Ta₂O₅ layer, or a multilayer film composed ofthese layers, for example, may be used as the antireflective film 114.Providing the DBR 170 on the side of the first reflective surface 160and second reflective surface 162 enables high reflectance to beobtained.

The DBR 170 may be provided to at least one of the side of the firstreflective surface 160 and the side of the second reflective surface162. In the example shown in FIG. 2, the DBR 170 is provided to the sideof the first reflective surface 160 and the side of the secondreflective surface 162. The DBR 170 can be composed of a plurality ofgrooves 172 arranged at a predetermined interval. The planar shape ofthe grooves 172 is rectangular, for example. The bottom surface of thegrooves 172 is preferably positioned lower than the lower side surfaceof the active layer 106. In the example shown in FIG. 3, the bottomsurface of the grooves 172 is positioned lower than the upper surface ofthe substrate 102. The insides of the grooves 172 may be hollow (air) orfilled with an insulation material. The filling material may also be asemiconductor or other conductive material insofar as the material iselectrically separated from the gain region 140. Four grooves 172 areprovided in the example shown, but this number is not limiting. A DBR170 having higher reflectance can be obtained by increasing the numberof grooves 172.

In the DBR 170 on the side of the first reflective surface 160, thegrooves 172 may be arranged so that the size of the width “a” of thegrooves 172 is (2m_(a)+1)λ/(4n_(a) cos θ₃′) or (2m_(a)+1)λ/(4n_(a) cosθ₄′), and the size of the interval “b” of the grooves 172 is(2m_(b)+1)λ/(4n_(b) cos θ₃) or (2m_(b)+1)λ/(4n_(b) cos θ₄). In theseexpressions, m_(a) and m_(b) are integers equal to 0 or higher, λ is thewavelength of the light generated by the gain region 140, n_(a) is theeffective refractive index of the vertical cross-section of the grooves172, and n_(b) is the effective refractive index of the verticalcross-section in the region in which the grooves 172 are not formed. Theangles θ₃′ and θ₄′ are refraction angles in a case of incidence on thefirst reflective surface 160 at the angle θ₃ or θ₄ from the gain region140, wherein θ₃′=sin⁻¹ ((n_(b)/n_(a))sin θ₃), and θ₄′=sin⁻¹((n_(b)/n_(a))sin θ₄). Grooves 172 having a predetermined width a areprovided at a predetermined interval b, whereby low-refracting regionsand high-refracting regions are provided in alternating fashion. The DBR170 can thereby be formed. On the other hand, in the DBR 170 provided tothe side of the second reflective surface 162, regardless of thedirection of the gain region, the grooves are preferably arranged sothat the size of the width a is (2m_(a)+1)λ/4n_(a), and the size of theinterval b is (2m_(b)+1)λ/4n_(b). The reason for this is that in thefirst reflective surface 160, most of the light that passes through thereflective surface propagates in the directions of the refraction anglesθ₃′ and θ₄′, whereas in the second reflective surface 162, most of thelight that incidents the reflective surface is light that is diffusedand not totally reflected, and is therefore not directional.

FIG. 5 is a graph showing the wavelength dependence of reflectance forthe vertically incident component in the second reflective surface 162when the size of the width a of the grooves 172 is 472.5 nm (m_(a)=1)and the size of the interval b of the grooves 172 is 423.64 nm(m_(b)=4). In this instance, diffraction in the direction perpendicularto the paper surface in FIG. 2 is ignored. The size of each of the widtha and interval b of the grooves 172 is 400 nm or greater, which is asize that can be formed by a photolithography technique. As shown inFIG. 5, an adequate reflection spectrum can be obtained even when theDBR 170 is of a size that allows formation by a photolithographytechnique. Consequently, the DBR 170 can easily be manufactured using aphotolithography technique. The size of the width a and the size of theinterval b can be made to approach a ratio of 1:1 by satisfying thefollowing relationship: m_(a)=n_(a)/(n_(b)×m_(b)). The DBR 170 canthereby be easily manufactured when an interference exposure or othermethod is used as well.

The second cladding layer 108 is formed on the active layer 106. Thesecond cladding layer 108 is composed of a second conductive (p-type,for example) semiconductor, for example. A p-type AlGaInP layer, forexample, can be used as the second cladding layer 108.

For example, a pin diode is formed by a p-type second cladding layer108, the active layer 106 not doped with an impurity, and an n-typefirst cladding layer 104. The first cladding layer 104 and the secondcladding layer 108 are each layers having a larger forbidden band gapwidth and a smaller refractive index than the active layer 106. Theactive layer 106 has the function of amplifying light. The firstcladding layer 104 and second cladding layer 108 sandwich the activelayer 106 and have the function of confining in injection carriers(electrons and positive holes) and light.

In the light emitting device 100, when a forward bias voltage of the pindiode is applied across the first electrode 120 and second electrode122, recombination of electrons and holes occurs in the gain region 140of the active layer 106. Light is generated by this recombination. Thenstimulated emission that originates in the recombination occurs, and theintensity of the light is amplified within the gain region 140. Forexample, a portion of the light generated by the first portion 142 ofthe gain region 140 is reflected by the first reflective surface 160 andthe second reflective surface 162 in sequence and emitted as secondemitted light 22 from the second end surface 152, and the lightintensity is amplified during this process. In the same manner, aportion of the light generated by the second portion 144 is reflected bythe second reflective surface 162 and the first reflective surface 160in sequence and emitted as first emitted light 20 from the first endsurface 151, and the light intensity is amplified during this process.Some of the light generated by the first portion 142 is emitted as firstemitted light 20 directly from the first end surface 151. In the samemanner, some of the light generated by the second portion 144 is emittedas second emitted light 22 directly from the second end surface 152.These portions of light are amplified in each of the gain portions inthe same manner. Moreover, a portion of the light generated by the thirdportion 146 is reflected at the first reflective surface 160, forexample, and emitted as first emitted light 20. A portion of the lightgenerated by the third portion 146 is reflected at the second reflectivesurface 162, for example, and emitted as second emitted light 22. Theintensity of these portions of light is also amplified in theintervening gain portions. At least a portion of the light that isgenerated by the gain region 140 and that passes through the firstreflective surface 160 or the second reflective surface 162 may also bereturned to the gain region 140 by the DBR 170 and be amplified.

The contact layer 110 is formed on the second cladding layer 108 asshown in FIG. 3. A layer that is in ohmic contact with the secondelectrode 122 can be used as the contact layer 110. The contact layer110 is composed of a second conductive semiconductor, for example. Ap-type GaAs layer or the like, for example can be used as the contactlayer 110.

The contact layer 110 and a portion of the second cladding layer 108 canform columnar semiconductor stacks (hereinafter referred to as “columnarparts”) 130. The planar shape of the columnar parts 130 may be the sameas that of the gain region 140 in the region in which the secondelectrode 122 is formed. Specifically, the current path between theelectrodes 120, 122 is determined by the planar shape of the columnarparts 130, for example, and as a result, the planar shape of the gainregion 140 is determined. Although not shown in the drawings, thecolumnar parts 130 can also be composed of the contact layer 110, aportion of the second cladding layer 108, a portion of the active layer106, and a portion of the first cladding layer 104 in the region inwhich the second electrode 122 is formed, for example.

The insulation part 112 can be provided on the second cladding layer 108and on the side of the columnar parts 130, as shown in FIGS. 1 and 3.The insulation part 112 can be adjacent to the side surface of thecolumnar parts 130. The upper surface of the insulation part 112 may becontinuous with the upper surface of the contact layer 110, for example.An SiN layer, SiO₂ layer, polyimide layer, or other layer, for example,can be used as the insulation part 112. When these materials are used asthe insulation part 112, the current between the electrodes 120, 122avoids the insulation part 112 and can flow through the columnar parts130 sandwiched by the insulation part 112. The insulation part 112 maybe provided at least to the region of the peripheral edges of thecolumnar parts 130 as viewed two-dimensionally. In the example shown inFIG. 2, the insulation part 112 may be provided in the same region asthe second electrode 122, other than in the regions in which thecolumnar parts 130 are formed.

Although not shown in the drawing, the insulation part 112 may cover theside surface forming the columnar parts 130 other than the surface fromthe first end 151 to the sixth end surface 156. The insulation part 112may have a lower refractive index than the active layer 106. In thiscase, the effective refractive index of the vertical cross-section ofthe portion in which the insulation part 112 is formed is smaller thanthe effective refractive index of the portion in which the insulationpart 112 is not formed, i.e., the vertical cross-section of the portionin which the columnar parts 130 are formed. Light can thereby beefficiently confined within the gain region 140 in the planar direction.A configuration may also be adopted in which the insulation part 112 isnot provided. The insulation part 112 may also be air, for example. Inthis case, a configuration may be adopted in which the active layer 106and the first cladding layer 104 are not included in the columnar parts130. A configuration may also be adopted in which the second electrode122 described hereinafter is formed so as not to directly contact theactive layer 106 and the first cladding layer 104.

The first electrode 120 is formed on the entire lower surface of thesubstrate 102. The first electrode 120 can be adjacent to a layer(substrate 102 in the example shown in the drawing) that is in ohmiccontact with the first electrode 120. The first electrode 120 iselectrically connected to the first cladding layer 104 via the substrate102. The first electrode 120 is one of the electrodes for driving thelight emitting device 100. An electrode in which a Cr layer, an AuGelayer, a Ni layer, and an Au layer are layered in sequence from thesubstrate 102, for example, can be used as the first electrode 120. Aconfiguration may also be adopted in which a second contact layer (notshown) is provided between the first cladding layer 104 and thesubstrate 102, the second contact layer is exposed by dry etching or thelike, and the first electrode 120 is provided on the second contactlayer. A single-sided electrode structure can thereby be obtained. Thisarrangement is particularly effective when the substrate 102 is aninsulator.

The second electrode 122 can be formed on the entire surface of thecontact layer 110 and insulation part 112, as shown in FIG. 3. When theactive layer 106 or both the active layer 106 and first cladding layer104 are included in the columnar parts 130, and the insulation part 112is not provided, the second electrode 122 are preferably formed inlocalized fashion only on the contact layer 110 (columnar parts 130),for example, so that there is no direct electrical connection betweenthe second electrode 122 and the active layer 106 or first claddinglayer 104. The second electrode 122 is electrically connected to thesecond cladding layer 108 via the contact layer 110. The secondelectrode 122 is the other electrode for driving the light emittingdevice 100. An electrode in which a Cr layer, an AuZn layer, and an Aulayer are layered in sequence from the contact layer 110, for example,can be used as the second electrode 122. The surface of contact betweenthe second electrode 122 and the contact layer 110 has the same planarshape as the gain region 140.

The light emitting device 100 of the present embodiment can be used asthe light source of a projector, display, illumination device,measurement device, or the like, for example. The same applies to theembodiments described hereinafter.

The light emitting device 100 has the following characteristics, forexample.

In the light emitting device 100, laser oscillation of light generatedby the gain region 140 can be suppressed or prevented, as describedabove. Speckle noise can therefore be reduced. Furthermore, in the lightemitting device 100, the light generated by the gain region 140 can beamplified while propagating in the gain region 140, and be emitted tothe outside. Consequently, a higher output than that of the conventionalLED can be obtained. Through the present embodiment as described above,a novel light emitting device can be provided that has high output andthe capability of reducing speckle noise.

In the light emitting device 100, the first emitted light 20 and secondemitted light 22 emitted from the first end surface 151 and second endsurface 152, respectively, can proceed in the same direction. An opticalsystem of a subsequent stage not shown in the drawing can thereby bereduced in size relative to a case in which two emitted lights proceedin divergent directions, for example.

In the light emitting device 100, a portion of the light generated bythe first portion 142 of the gain region 140 is reflected at the firstreflective surface 160 and the second reflective surface 162, and can beamplified while propagating in the third portion 146 and second portion144 as well. The same applies for a portion of the light generated bythe second portion 144. Consequently, depending on the light emittingdevice 100 of the present embodiment, since the distance over which thelight intensity is amplified is increased relative to a case in which noreflection occurs at the first reflective surface 160 on the secondreflective surface 162, high light output can be obtained.

In the light emitting device 100 of the present embodiment, the DBR 170composed of a plurality of grooves 172 can be provided to at least oneof the side of the first reflective surface 160 and the side of thesecond reflective surface 162. Consequently, depending on the lightemitting device 100, the size of the device can be reduced relative to acase in which a mirror part is provided outside the light emittingdevice, for example. Furthermore, since the DBR 170 can be manufacturedby a planar process, the amount of raw materials used can be reducedwhile production properties are enhanced relative to a case in which adielectric minor is formed after cleaving each chip, for example.

1.2. A method for manufacturing the light emitting device 100 of thefirst embodiment will next be described with reference to the drawings.

FIGS. 6 through 8 are schematic sectional views showing the steps formanufacturing the light emitting device 100, and correspond to thesectional view shown in FIG. 3.

As shown in FIG. 6, the first cladding layer 104, the active layer 106,the second cladding layer 108, and the contact layer 110 are firstformed in sequence on the substrate 102 by epitaxial growth. Examples ofepitaxial growth methods that can be used is MOCVD (Metal OrganicChemical Vapor Deposition), MBE (Molecular Beam Epitaxy), and the like.

The contact layer 110 and the second cladding layer 108 are thenpatterned as shown in FIG. 7. A photolithography technique, etchingtechnique, or other technique, for example, is used for patterning. Thecolumnar parts 130 and grooves 172 having about the same depth as thecolumnar parts 130 are thereby formed.

The grooves 172 are then etched to a predetermined depth, as shown inFIG. 8. This etching is performed in the same manner as in the stepshown in FIG. 7. The grooves 172 constituting the DBR 170 are therebyformed. In the steps described above, the grooves 172 are formed byperforming additional etching after being patterned at the same time asthe columnar parts 130. However, the grooves 172 may also be formed by asingle step of patterning the contact layer 110, second cladding layer108, active layer 106, first cladding layer 104, and substrate 102 afterthe columnar parts 130 are formed. Misalignment of the etching due toalignment error of the photomask or other conditions can thereby beprevented relative to a case in which additional etching is performed.

As shown in FIG. 3, the insulation part 112 is then formed so as tocover the side surfaces of the columnar parts 130. Specifically, aninsulation layer (not shown) is first formed above the second claddinglayer 108 (including on the contact layer 110) by CVD (Chemical VaporDeposition), coating application, or another method, for example. Theupper surface of the contact layer 110 is then exposed by an etchingtechnique or the like, for example. The insulation part 112 can beformed by the process described above. In the present step, the grooves172 can also be embedded in the insulation layer. A configuration mayalso be adopted in which the region of the grooves 172 is covered by aresist film (not shown), and the insulation layer is thereby notembedded in the grooves 172.

The second electrode 122 is then formed on the insulation part 112 andcontact layer 110 constituting the columnar parts 130, as shown in FIG.3. The second electrode 122 can be formed in the desired shape by aphotolithography technique by covering a predetermined region with aresist film (not shown), and then performing vacuum deposition andlift-off, for example. A region larger than that of the grooves 172 ispreferably covered by a resist film or the like, for example, so thatthe electrode material does not enter the grooves 172 and short-circuitthe region in which the DBR 170 is formed.

The first electrode 120 is then formed below the lower surface of thesubstrate 102. The method for fabricating the first electrode 120 is thesame as the method described above for fabricating the second electrode122, for example. The sequence in which the first electrode 120 and thesecond electrode 122 are formed is not particularly limited.

The antireflective film 114 is then formed on the entire surface of thefirst side surface 105, as shown in FIG. 2. The antireflective film 114is formed by CVD (Chemical Vapor Deposition), sputtering, ion assisteddeposition, or another method, for example.

The light emitting device 100 can be manufactured by the processdescribed above.

1.3 A modification of the light emitting device of the presentembodiment will next be described. Only those aspects that differ fromthe example of the light emitting device 100 shown in FIGS. 1 through 3described above will be described, and no redundant description of thesame aspects will be given.

(1) A first modification will first be described.

FIG. 9 is a schematic plan view showing the light emitting device 200 ofthe present modification. FIG. 10 is a sectional view along line X-X ofFIG. 9. The plan view shown in FIG. 9 corresponds to FIG. 2.

In the example of the light emitting device 100, a case was described inwhich the DBR 170 is provided to the sides of the reflective surfaces160, 162. In the present modification, however, photonic crystal regions180 may be provided to the sides of the reflective surfaces 160, 162.

The photonic crystal regions 180 are composed of a plurality of holes182 arranged periodically in a predetermined lattice arrangement in thein-plane direction of the active layer 106. Specifically, the photoniccrystal regions 180 have a two-dimensional photonic crystal structure inwhich a periodic refractive index distribution is formed in the planardirection. The shape of the holes 182 is columnar, for example. Thebottom surface of the holes 182 may be positioned lower than the lowerside surface of the active layer 106, for example. The bottom surface ofthe holes 182 may be higher than the upper surface of the active layer106 insofar as an adequate number of periods is provided. In the exampleshown in the drawing, a plurality of holes 182 is arranged at equalintervals in a square lattice pattern. The holes 182 may be arranged ina triangular lattice, a rectangular lattice, a honeycomb lattice, acircular lattice, or other arrangement, for example. The holes 182 havea columnar shape in the example shown. The planar shape of the holes 182may be circular, elliptical, triangular, square, or another shape. Whenthe design wavelength is 630 nm, the size of the interval d of the holes182 may be about 231 nm, and the size of the radius r of the openings ofthe holes 182 may be about 134 nm. An adequate reflection spectrum canbe obtained even when the photonic crystal regions 180 is of a size thatallows formation by a photolithography technique (including aninterference exposure technique, immersion exposure technique, or othertechnique). The interior of the holes 182 may be hollow or filled withan insulating material. The photonic crystal region may include a regionhaving a periodic photonic crystal structure, or a cylindrical polarcoordinate lattice, a quasi-photonic crystal structure having aquasi-period photonic crystal, or other structure, for example. Highreflectance can be obtained from the first reflective surface 160 andthe second reflective surface 162 by providing the photonic crystalregion.

The holes 182 may be formed using a photolithography technique, etchingtechnique, or other technique, for example. The photonic crystal regions180 composed of the holes 182 can thereby be formed.

Through the present modification, the photonic crystal regions 180 canbe provided instead of the DBR 170 on the sides of the reflectivesurfaces 160, 162. A novel light emitting device can thereby be providedthat has high output and the capability of reducing speckle noise, thesame as in the first embodiment described above.

(2) A second modification will next be described.

FIG. 11 is a schematic plan view showing the light emitting device 300according to the present modification. The plan view shown in FIG. 11corresponds to FIG. 2.

In the example of the light emitting device 100, a case was described inwhich a single gain region 140 is provided. In the present modification,however, a plurality (two in the example shown in FIG. 11) of gainregions 140 may be provided. A DBR 170 may be provided beside each ofthe reflective surfaces 160, 162 of the gain regions 140. Photoniccrystal regions 180 may also be formed instead of the DBR 170. Since theDBR 170 and the photonic crystal regions 180 can be manufactured by aplanar process as described above, an array can more easily be formedthan in a case in which a dielectric mirror is formed or cleaved foreach chip, for example.

Through the present modification, a higher output can be obtained fromthe light emitting device as a whole in comparison to the light emittingdevice 100.

(3) A third modification will next be described.

The light emitting device 100 was described as being an InGaAlP-typelight emitting device, but any material from which a light emitting gainregion can be formed may be used in the present modification. Forexample, an AlGaN, InGaN, GaAs, InGaAs, GaInNAs, ZnCdSe, or other typeof semiconductor material may be used as the semiconductor material. Inthe present modification, a GaN substrate or the like, for example, maybe used as the substrate 102. An organic material or the like, forexample, may also be used in the present modification.

The modifications described above are merely examples, and are notlimiting. For example, the modifications can also be appropriatelycombined. These modifications can also be applied as needed to theembodiments described hereinafter.

2. Second Embodiment

2.1 The light emitting device 400 according to a second embodiment willnext be described, but the examples described below are not limiting.

FIG. 12 is a schematic plan view showing the light emitting device 400,and FIG. 13 is a sectional view along line XIII-XIII of FIG. 12. Thesame reference numerals are used to refer to members of the lightemitting device 400 according to the second embodiment that have thesame functions as constituent members of the light emitting device 100of the first embodiment, and no detailed description thereof will begiven.

As shown in FIGS. 12 and 13, the light emitting device 400 includes thefirst cladding layer 104, the active layer 106, and the second claddinglayer 108. The light emitting device 400 may also include the substrate102, contact layer 110, antireflective film 114, first electrode 120,second electrode 122, and DBR 170.

The second cladding layer 108 may be formed on the active layer 106. Thecontact layer 110 may be formed on the second cladding layer 108. Asshown in FIG. 13, the second cladding layer 108 and the contact layer110 do not form columnar parts 130.

The second electrode 122 is formed on the contact layer 110. The secondelectrode 122 is electrically connected to the second cladding layer 108via the contact layer 110. The lower surface of the second electrode 122has the same planar shape as the gain region 140, as shown in FIG. 12.In the example shown, the current path between the electrodes 120, 122is determined by the planar shape of the connection region of the secondelectrode 122 and the contact layer 110, and as a result, the planarshape of the gain region 140 can be determined. In the example shown inthe drawing, both the upper and lower surface of the second electrode122 have the same planar shape as the gain region 140.

Depending on the present embodiment, a novel light emitting device canbe provided that has high output and the capability of reducing specklenoise, the same as in the first embodiment described above.

2.2. An example of the method for manufacturing the light emittingdevice 400 of the second embodiment will next be described withreference to the drawings, but the example described below is notlimiting. Only those aspects that differ from the method formanufacturing the light emitting device 100 of the first embodimentdescribed above will be described, and no detailed description of thesame aspects will be given.

FIG. 14 is a schematic sectional view showing the steps formanufacturing the light emitting device 400, and corresponds to thesectional view shown in FIG. 13.

The first cladding layer 104, active layer 106, second cladding layer108, and contact layer 110 are first formed on the substrate 102.

The grooves 172 are then formed. The grooves 172 are formed using aphotolithography technique, etching technique, or other technique, forexample.

The second electrode 122 is then formed, as shown in FIG. 14. The secondelectrode 122 can be formed in the desired shape by a photolithographytechnique by covering a predetermined region with a resist film (notshown), and then performing vacuum deposition and lift-off, for example.

The first electrode 120 and the antireflective film 114 are then formed.

The light emitting device 400 can be manufactured by the processdescribed above.

2.3 A modification of the light emitting device of the presentembodiment will next be described. Only those aspects that differ fromthe example of the light emitting device 400 shown in FIGS. 12 and 13described above will be described, and no description of the sameaspects will be given.

FIG. 15 is a schematic sectional view showing the light emitting device500 according to the present modification. The sectional view shown inFIG. 15 corresponds to the sectional view shown in FIG. 13.

In the example of the light emitting device 400, a case was described inwhich the upper surface and the lower surface of the second electrode122 both have the same planar shape as the gain region 140, as shown inFIGS. 12 and 13. In the present modification, however, the upper surfaceof the second electrode 122 may have a different planar shape than thegain region 140, as shown in FIG. 15. In the present modification,insulation layers 502 having opening sections are formed on the contactlayer 110, and the second electrode 122 may be formed so as to fill theopening sections. The insulation layers 502 are formed on the peripheryof the gain region 140, for example, as viewed two-dimensionally. Thesecond electrode 122 is formed in the opening sections and on theinsulation layers (502. In the present modification, the lower surfaceof the second electrode 122 has the same planar shape as the gain region140, and the upper surface of the second electrode 122 is the entiresurface above the insulation layers 502 and these opening sections.

An SiN layer, SiO₂ layer, polyimide layer, or other layer may be used asthe insulation layers 502. The insulation layers 502 are formed by CVD,coating application, or another method, for example.

Through the present modification, since the volume of the secondelectrode 122 increases relative to the example of the light emittingdevice 400, a light emitting device 500 can have excellent heatdissipation properties.

Modifications are not necessarily limited by the examples describedabove. These modifications or the examples of the light emitting device100 may also be applied as needed to the embodiments described above.

3. Embodiments of the present invention are described in detail above,but it will be readily apparent to one skilled in the art that numerousmodifications of the present invention are possible in a range that doesnot depart from the new matter and effects of the present invention. Allsuch modifications are accordingly encompassed by the present invention.

What is claimed is:
 1. A light emitting device comprising: an activelayer forming a gain region that generates light; a first cladding layerand a second cladding layer that sandwich the active layer and confinethe light in the active layer; and a first reflective part and a secondreflective part that are provided next to the gain region so as toreflect the light; wherein each of the first reflective part and thesecond reflective part changes a first light traveling direction of thelight and a second light traveling direction of the light as viewed froma stacking direction of the first cladding layer, the active layer, andthe second cladding layer, the gain region extends continuously from afirst end provided at a first side surface of the active layer to asecond end provided at the first side surface, and the light is emittedfrom the first end as first light propagating in a first light emittingdirection having a first angle with respect to the first side surface,and the light is emitted from the second end as second light propagatingin a second light emitting direction having a second angle with respectto the first side surface.
 2. The light emitting device according toclaim 1, wherein the first and second angles are the same.
 3. The lightemitting device according to claim 1, wherein the first and second lightemitting directions are parallel to each other.
 4. The light emittingdevice according to claim 1, wherein the gain region has a first portionthat extends between the first reflective part and the first end in afirst extending direction, and a second portion that extends between thesecond reflective part and the second end in a second extendingdirection, and the first and second extending directions are the same.5. The light emitting device according to claim 1, wherein the firstreflective part and the second reflective part are provided inwardlyrelative to the first side surface.
 6. The light emitting deviceaccording to claim 1, wherein at least one of the first reflective partand the second reflective part includes a distributed Bragg reflector.7. The light emitting device according to claim 6, wherein thedistributed Bragg reflector includes a plurality of grooves arranged ata predetermined interval.
 8. The light emitting device according toclaim 7, wherein a bottom surface of each of the grooves is recessedrelative to a lower surface of the active layer.
 9. The light emittingdevice according to claim 1, wherein at least one of the firstreflective part and the second reflective part includes a photoniccrystal region.
 10. The light emitting device according to claim 9,wherein the photonic crystal region includes a plurality of holesarranged periodically in a lattice arrangement in the in-plane directionof the active layer.
 11. The light emitting device according to claim10, wherein each of the plurality of holes has a columnar shape, and abottom surface of each of the holes is recessed relative to a lowersurface of the active layer.
 12. The light emitting device according toclaim 1, wherein a first normal direction with respect to a firstreflection surface of the first reflective part and a second normaldirection with respect to a second reflection surface of the secondreflective part are orthogonal to each other.
 13. The light emittingdevice according to claim 12, wherein the light generated by the gainregion is totally reflected by the first reflective part and the secondreflective part.
 14. The light emitting device according to claim 1,wherein an antireflective film is provided to the first side surface.15. The light emitting device according to claim 1, wherein the gainregion is provided in as a plurality of gain regions.
 16. The lightemitting device according to claim 1, further comprises: a firstelectrode electrically connected to the first cladding layer; and asecond electrode electrically connected to the second cladding layer.17. A light emitting device comprising: an active layer forming a gainregion that generates light; a first cladding layer and a secondcladding layer that sandwich the active layer and confine the light inthe active layer; and a first reflective part and a second reflectivepart that are provided next to the gain region so as to reflect thelight; wherein the gain region has an elongated strip shape that turnsat both the first reflective part and the second reflective part asviewed from a stacking direction of the first cladding layer, the activelayer, and the second cladding layer, and the gain region extendscontinuously from a first end provided at a first side surface of theactive layer to a second end provided at the first side surface, and thelight is emitted from the first end as first light propagating in afirst light emitting direction having a first angle with respect to thefirst side surface, and the light is emitted from the second end assecond light propagating in a second light emitting direction having asecond angle with respect to the first side surface.
 18. The lightemitting device according to claim 17, wherein the first and secondangles are the same, and the first and second light emitting directionsare parallel to each other.
 19. The light emitting device according toclaim 17, wherein the gain region has a first portion that extendsbetween the first reflective part and the first end in a first extendingdirection, and a second portion that extends between the secondreflective part and the second end in a second extending direction, andthe first and second extending directions are the same.
 20. The lightemitting device according to claim 17, wherein a first normal directionwith respect to a first reflection surface of the first reflective partand a second normal direction with respect to a second reflectionsurface of the second reflective part are orthogonal to each other. 21.A light emitting device comprising: an active layer forming a gainregion that generates light; a first cladding layer and a secondcladding layer that sandwich the active layer and confine the light inthe active layer; and a first reflective part and a second reflectivepart that are provided next to the gain region so as to reflect thelight; wherein the gain region has a U-shape, and the gain regionextends continuously from a first end provided at a first side surfaceof the active layer to a second end provided at the first side surface,and the light travels in a first light traveling direction from thefirst reflective part toward the first end in the gain region, the lighttravels in a second light traveling direction from the second reflectivepart toward the second end in the gain region, and the first lighttraveling direction and the second light traveling direction areparallel to each other.